additional localized structures are produced that can be seen propagating to the left. These structures could later cause trouble, but looking at region (b) we see that in fact they just pass through other structures that they meet without any adverse effect.

Region (c) shows what happens when the information corresponding to one element in a block passes through the kind of object produced in region (a). The number of localized structures that represent the element is reduced from twelve to four, but the spacings of these structures continue to specify its color. Region (d) then shows how the object in region (c) comes to an end when the beginning of the block separator from the next step arrives.

Region (e) shows how the information corresponding to a black element in a block is actually converted to a new black element in the sequence produced by the cyclic tag system. What happens is that the four localized structures corresponding to the element in the block collide with four other localized structures travelling in the opposite direction, and the result is four stationary structures that correspond to the new element in the sequence.

Region (f) shows the same process as region (e) but for a white element. The fact that the element is white is encoded in the wider spacing of the structures coming from the right, which results in narrower spacing of the stationary structures.

Region (g) shows the analog of region (a), but now for a white element instead of a black one. The region begins much like region (a), except that the four localized structures at the top are more narrowly spaced. Starting around the middle of the region, however, the behavior becomes quite different from region (a): while region (a) yields an object that allows information to pass through, region (g) yields one that stops all information, as shown in regions (h) and (i).

Note that even though they begin very differently, regions (d) and (i) end in the same way, reflecting the fact that in both cases the system is ready to handle a new block, whatever that block may be.

The pictures on the last few pages [683, 684, 685, 686] were all made for a cyclic tag system with a specific underlying rule. But exactly the same principles